This invention relates to a printing machine and is more particularly directed to a printing mechanism having a parity or check digit generated in accordance with a predetermined algorithm.
Recently, the U.S. Postal Service developed the Postal Numeric Encoding Technique (POSTNET) to provide an optimized bar code system for encoding ZIP CODE information on letter mail. This system was designed so the encoded information may be reliably read and decoded by state of the art optical reading systems.
In an ideal situation, an encoded bar code representing the full ZIP code and a parity character would be printed on all mail pieces by each business mailer. The large business mailers will have automated electronic equipment which will imprint the bar codes on the individual mail pieces. Normally, this equipment would be fully automated and would optically read the zip code from a mail piece, translating the zip code to an encoded bar code, and then imprint the encoded bar code on the mail piece. However, many small users would not have the required mail volume to purchase or lease this sophisticated equipment to imprint the POSTNET bar code. A less costly system is desired for those small business mailers having relatively few mail pieces. An inexpensive system would also be useful to large business mailers as automated systems might miss several pieces or be unable to read them. In these cases, the inexpensive manually operable system could individually print the bar code corresponding to the ZIP code of the unread mail piece.
The elements of the POSTNET bar code are bars and half bars representing binary 1's and 0's respectively. The code is a character by character representation of a five or nine digit zip code. Each time that a zip code is printed in bar code format, one additional character is encoded along with the zip code. This character, which is part of the error detection system, is called a parity bit or check digit.
The check digit in the POSTNET system is always selected so that the sum of all the digits in the bar code field is an integral multiple of ten. For example, the nine-digit zip code 12345-6789 is to be encoded in the POSTNET format. Summing the nine digits yields 45. A check digit of 5 will result in the sum of the 10 digits being an integral multiple of 10.
In the past, there have been numbering machines with means for generating a self-checking number or check digit. One example is found in U.S. Pat. No. 3,815,495 entitled "Modulus 10 Numbering Machine". This device uses various sensors and solenoids operated from a cam to increment and present the correct parity digit for printing. The system illustrated in U.S. Pat. No. 3,815,495 is extremely complex, requiring numerous sensors, cams, and mechanical and electrical connections in order to operate.
In U.S. Pat. No. 4,085,670 entitled "Check Digit Numbering Mechanism", a series of solenoids and movable armatures are also utilized. Again a complex electro-mechanical system is required for proper functioning.
It should be recognized that in both of these patents, the numbers which are printed on the documents are the numeric numbers which are desired. None of these devices contemplated or illustrated the use of printing bar code equivalents to the numbers or the check digit character generated.